Process for Preparing Substituted Biphenylanilides

ABSTRACT

The present invention relates to a process for preparing substituted biphenylanilides of the formula I 
     
       
         
         
             
             
         
       
     
     which comprises reacting a compound of formula II 
     
       
         
         
             
             
         
       
     
     in the presence of a base and of a palladium catalyst selected from the group of: a) palladium-triarylpliosphine or -trialkylphosphine complex with palladium in the zero oxidation state, b) salt of palladium in the presence of triarylphospine or trialkylphosphine as a complex ligand or c) metallic palladium, optionally applied to support, in the presence of triarylphosphine or trialkylphosphine, in a solvent, with a diphenylborinic acid according to formula (III)

The present invention relates to a process for preparing substituted biphenylanilides of the formula I

in which the substituents are defined as follows:

Het is a heterocyclyl-residue selected from

-   -   wherein “#” indicates the substituted position of the residue;

-   X is hydrogen fluorine or chlorine;

-   R¹ is C₁—C₆-haloalkyl,;

-   R² is cyano, nitro, halogen, C₁—C₆-alkyl, C₁—C₆-alkenyl,     C₁—C₆-alkynyl, C₁—C₆-alkoxy,

-   C₁—C₆-haloalkyl, (C₁—C₆-alkyl)carbonyl or phenyl;

-   n is 1 , 2 or 3, where in case that n is 2 or 3, the R² radicals may     also be different, which comprises reacting a compound of formula II

-   -   in which Hal is halogen and X and Het are as defined above, in         the presence of a base and of a palladium catalyst selected from         the group of: a) palladium-triarylphosphine or         -trialkylphosphine complex with palladium in the zero oxidation         state, b) salt of palladium in the presence of triarylphospine         or trialkylphosphine as a complex ligand or c) metallic         palladium, optionally applied to support, in the presence of         triarylphosphine or trialkylphosphine, in a solvent, with a         diphenylborinic acid according to formula (III)

-   -   in which R² and n are as defined above, where the         triarylphosphines or trialkylphosphines used may be substituted.

Tetrahedron Lett. 32, page 2277 (1991 ) states that the coupling reaction between phenylboronic acid and chlorobenzene with use of the [1 ,4-bis(diphenylphosphine)-butane]palladium(ll) dichloride catalyst proceeds with a yield of only 28%.

EP-A 0 888 261 discloses a process for preparing nitrobiphenyls by reacting chloronitrobenzenes with a phenylboronic acid in the presence of a palladium catalyst and of a base. In this process, a very high catalyst concentration is necessary.

WO 2006/092429 and WO 2007/138089 each pertain to a process for preparing substituted biphenyls by coupling substituted diphenylborinic acids with dihaloarylcompounds in presence of a palladium catalyst.

It was therefore an object of the present invention to provide an economically viable process which can be implemented on the industrial scale for regioselectively preparing substituted biphenylanilides, which works with a reduced palladium catalyst concentration.

Accordingly, the process defined at the outset has been found.

The diphenylborinic acid (III) is obtained by reaction of optionally substituted phenylmagnesiura chloride V with trialkyl borate, preferably trimethyl borate, in tetrahydrofuran as a solvent according to WO 2007/138089 as described by scheme 1.

-   R⁴ is C₁—C₄-alkyl, preferably methyl.

Essential for a high yield of diphenylborinic acid (III) is the use of only 0.7 eq. of trialkyl borate based on the substituted chlorobenzene (IV) used. Use of 1.1 eq. of trialkyl borate gives rise to phenylboronic acid as described in EP-A 0 888 261.

The reaction temperature in this process stage is from 20 to 60° C., preferably from 40 to 50° C.

The substituted biphenyls prepared by the present process have the following preferred substituents, in each case both individually and in combination.

Het is a heterocyclyl-residue selected from

-   -   wherein “#” indicates the substituted position of the residue;

-   R¹ is trifluoromethyl or difluoromethyl, more preferably     difluoromethyl;

-   R² is cyano, nitro, fluorine, chlorine, bromine, methyl, ethyl,     propyl, butyl, allyl, propargyl, methoxy, ethoxy, trifluoromethyl or     phenyl, more preferably fluorine, chlorine, methyl or methoxy, most     preferably fluorine or chlorine;

-   n is 1 or 2, preferably 2.

The subsequent homogeneously catalyzed Suzuki biaryl cross-coupling is carried out according to scheme 2.

Preference is given to starting from diphenylbormie acids of the formula (III) in which R2 and n are as defined above.

Further preferred starting materials are diphenylbormie acids (III) in which n is 1 or 2, in particular 2. Particularly preferred arc diphenylborinic acids (III) which are substituted in the 3- and 4-position or in 4-position only.

Very particular preference is given to di(2,3-difluoropheny)borinic acid, di(3,4-di-fluorophenyl)borinic acid, di(2,3-dichloroplienyl)borinic acid and in particular di(3,4-dichlorophenyl)borinic acid and (4-chlorophenyl)borinic acid as the starting compound (III).

Preference is given to starting from the following compounds (II):

N-(2-chloro-4-fluorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromo-4-fluorophenyl)-3-(difluoromethyl)-1-methyl-1 H-pyrazole-4-carboxamide, N-(2-chloro-4-fluorophenyl)-3-(trifluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromo-4-fluorophenyl)-3-(trifluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-chloro-6-fluorophenyl)-3-(difluoro-methyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromo-6-fluorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-chloro-6-fluorophenyl)-3-(trifluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromo-6-fluorophenyl)-3-(trifluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-chlorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-chlorophenyl)-3-(trifluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromophenyl)-3-(trifluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, 2-chloro-N-(2-chlorophenyl)pyridine-3-carboxamide, 2-chloro-N-(2-bromophenyl)pyridine-3-carboxamide particularly preferred are N-(2-chloro-4-fluorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromo-4-fluorophenyl)-3-(difluoromethyl)-1 -methyl-1H-pyrazole-4-carboxamide, 2-chloro-N-(2-chlorophenyl)pyridine-3-carboxamide and 2-chloro-N-(2-bromophenyl)pyridine-3-carboxamide.

Compounds according to formula (II) can be prepared as described in WO 03/070705. Using, for example, 1-methyl-3-(trifluoromethyl)-1H-pyrazole-4-carbonyl chloride and 2-bromo-4-fluoroaniline as starting materials and a base as illustrated by the following equation:

The compound (II) is used, based on the diphenylborinic acids (III) (diphenylborinic acid equivalents), normally in an equimolar amount, preferably with an up to 20 percent excess, in particular with an up to 50 percent excess. The bases used may be organic bases, for example tertiary amines. Preference is given to using, for example, triethylamine or dimethylcyclohexylamine. The bases used are preferably alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydrogen- carbonates, alkali metal acetates, alkaline earth metal acetates, alkali metal alkoxides and alkaline earth metal alkoxides, in a mixture and in particular individually. Particularly preferred bases are alkali metal hydroxides, alkaline earth metal hydroxides, alkali metal carbonates, alkaline earth metal carbonates and alkali metal hydrogencarbonates. Especially preferred bases are alkali metal hydroxides, e.g. sodium hydroxide and potassium hydroxide, and also alkali metal carbonates and alkali metal hydrogencarbonates, e.g. lithium carbonate, sodium carbonate and potassium carbonate. The base is used in the process according to the invention preferably with a fraction of from 100 to 500 mol %, more preferably from 150 to 400 mol %, based on the amount of diphenylborinic acid (III). Suitable palladium catalysts are palladium-ligand complexes with palladium in the zero oxidation state, salts of palladium in the presence of complex ligands, or metallic palladium optionally applied to support, preferably in the presence of complex ligands. Suitable complex ligands are uncharged ligands such as triarylphosphines and trialkylphosphines, which may optionally be substituted in the aryl rings, such as triphenylphosphine (TPP), di-1-adamantyl-n-butylphosphine, tri-tert-butylphosphine (TtBP) or 2-(dicyclohexylphosphino)biphenyl.

Furthermore, the literature has also described further particularly reactive complex ligands from other structural classes, including 1 ,3-bis(2,6-diisopropylphenyl)-4,5-H2- imidazolium chloride (cf., for example, G. A. Grasa et al. Organometallics 2002, 21 , 2866) and tris(2,4-di-tert-butylphenyl) phosphite (cf. A. Zapf et al, Chem. Eur. J. 2000, 6, 1830).

The reactivity of the complex ligands can be enhanced by adding a quaternary ammonium salt such as tetra-n-butylammonium bromide (TBAB) (cf., for example, D. Zim et al. Tetrahedron Lett. 2000, 41 , 8199). If required, the water solubility of the palladium complexes can be improved by various substituents such as sulfonic acid or sulfonate salt groups, carboxylic acid or carboxylate salt groups, phosphonic acid, phosphonium or phosphonate salt groups, peralkylammonium, hydroxy and polyether groups. Among the palladium-ligand complexes with palladium in the 0 oxidation state, preference is given to using tetrakis(triphenylphosphine)pallaclium and additionally tetrakis[tri(o-tolyl)phosphine]palladium. In the salts of palladium which are used in the presence of complex ligands, the palladium is normally present in the two positive oxidation state. Preference is given to using palladium chloride, palladium acetate, palladium acetylacetonate (Pd(acac)₂ ) or bisacetonitrilepalladium chloride. Particular preference is given to using palladium bisacetylacetonate (Pd(acac)₂).

In general, from 1 to 60, preferably from 1 to 25, equivalents of the aforementioned complex ligands, in particular triphenylphosphine and, are combined with one equivalent of the palladium salt.

In a most preferred embodiment of the invention palladium bisacetylacetonate and tri-tert-butylphosphine are used in equimolar amounts

EP-A 0 888 261 describes the use of from 2 to 6 equivalents of triphenylphosphine per equivalent of the palladium catalyst. The use of high ligand excesses is generally viewed in the literature as disadvantageous, since this is expected to result in inactivation of the catalytically active complex (cf., for example, J. Hassan et al, Chem. Rev. 2002, 102, 1359). It was thus surprising that this high triphenylphosphine use in combination with the low catalyst use led to an increase in the overall yield of the process of the present invention and accordingly to an improvement in the economic viability. Metallic palladium is used preferably in pulverized form or on a support material, for example in the form of palladium on activated carbon, palladium on alumina, palladium on barium carbonate, palladium on barium sulfate, palladium on calcium carbonate, palladium aluminosilicates such as montmorillonite, palladium on SiO₂ and palladium on calcium carbonate, in each case with a palladium content of from 0.5 to 12% by weight. In addition to palladium and the support material, these catalyst may comprise further dopants, for example lead.

When metallic palladium optionally applied to support is used, particular preference is given to also using the aforementioned complex ligands, in particular to the use of palladium on activated carbon in the presence of triphenylphosphine as a complex ligand, where the phenyl groups in the triphenylphosphine are preferably substituted by a total of from one to three sulfonate groups. In the process according to the invention, the palladium catalyst is used with a low fraction of from 0.001 to 1.0 mol %, preferably from 0.005 to 0.5 mol % or from 0.01 to 0.5 mol % and in particular from 0.005 to 0.05 mol %, based on the amount of compound (II)

The low use of a palladium salt in combination with a high use of a complex ligand constitutes a significant cost advantage of this process over the prior art processes.

The process according to the invention may be carried out in a biphasic system composed of aqueous phase and solid phase, i.e. the catalyst. In that case, the aqueous phase may also comprise a water-soluble organic solvent in addition to water.

Organic solvents suitable for the process according to the invention are ethers such as dimethoxyethane, (Methylene glycol dimethyl ether, tetrahydrofuran, dioxane and tert-butyl methyl ether, hydrocarbons such as n-hexane, n-heptane, cyclohexane, benzene, toluene and xylene, alcohols such as methanol, ethanol, 1-propanol, 2-propanol, ethylene glycol, 1 -butanol, 2-butanol and tert.-butanol, ketones such as acetone, ethyl methyl ketone and isobutyl methyl ketone, amides such as dimethylformamide, dimethylacetamide and N-methylpyrrolidone, in each case individually or in a mixture.

Preferred solvents are ethers such as dimethoxyethane, tetrahydrofuran and dioxane, hydrocarbons such as cyclohexane, toluene and xylene, alcohols such as ethanol, 1-propanol, 2-propanol, 1-butanol and tert.-butanol, in each case individually or in a mixture. In a particularly preferred variant of the process according to the invention, water, one or more water-insoluble and one or more water-soluble solvents are used, for example mixtures of water and dioxane, or water and tetrahydrofuran, or water, dioxane and ethanol, or water, tetrahydrofuran and methanol, or water, toluene and tetrahydrofuran, preferably water and tetrahydrofuran, or water, tetrahydrofuran and methanol.

The total amount of solvent is normally from 3000 to 500 g and preferably from 2000 to 700 g, per mole of the compound (II).

Appropriately, the process is carried out by adding the compound (II), the diphenyl-borinic acids (III), the base and the catalytic amount of the palladium catalyst to a mixture of water and one or more inert organic solvents, and stirring at a temperature of from 50° C. to 120° C., preferably from 70° C. to 110° C., more preferably from 90° C. to 100° C., for a period of from 1 to 50 hours, preferably from 2 to 24 hours.

Depending on the solvent and temperature used, a pressure of from 1 bar to 6 bar, preferably from 1 bar to 4 bar, is established. Preference is given to carrying out the reaction in water and tetrahydrofuran. The reaction may be carried out in customary apparatus suitable for such processes. On completion of reaction, palladium catalyst obtained as a solid is removed, for example by filtration, and the crude product is freed from the solvent or the solvents. In the case of products which are not fully water-soluble, water-soluble palladium catalysts or complex ligands are removed fully from the crude product in the separation of the water phase. Subsequently, further purification may be effected by methods which are known to those skilled in the art and are appropriate to the particular product, for example by recrystaliization, distillation, sublimation, zone melting, melt crystallization or chromatography.

In a further preferred embodiment of the invention the reaction is carried out in toluene or a mixture of water and toluene, such as a 1/1 mixture (water/toluene). On completion of the reaction product and catalyst can be separated by phase separation.

By the process according to the invention, it is possible to prepare, for example:

2-chloro-N-(4′-chlorobiphenyl-2-yl)pyridine-3-carboxamide, N-(3′,4′-diehlorobiphenyl-2-yl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(3′,4′-dichloro-5-fluorobiphenyl-2-yl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, 3-(trifluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(3′,4′-dichloro-5-fluorobiphenyl-2-yl)-3-(trifluoromethyl)-1-methyl-1 H-pyrazole-4-carboxamide.

The process according to the invention affords the compounds I in very high up to quantitative yields at very good purity. The substituted biphenyls obtainable by the process according to the invention are suitable as precursors for fungicidal crop protection active ingredients (cf. WO 03/070705).

EXAMPLES Example 1

Synthesis of Bis(3,4-dichlorophenyl)borinic acid

To a dry flask was added tribromoborane in DCM (13 ml, 13 mmol, 1M). This solution was cooled to −62 ° C., and bromo(3,4-dichlorophenyl)magnesium (50 ml, 25 mmol, 0.5M in THF) was added dropwise to the cold solution. The reaction mixture was allowed to warm to room temperature and stirred over night. The solvent was removed in vacuo, and the residue was dissolved in DCM and hydrolyzed by the slow addition of 1N HCl. The organic layer was separated and washed with brine, and the solvent was removed in vacuo. The resulting oil was purified by silica gel chromatography using 25% ethyl acetate as the eluent, which afforded the title compound as a solid (3.34 g, 10.4 mmol, 80% yield).

Example 2

Synthesis of N-(3′,4′-dichloro-5-fluorobiphenyl-2-yl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide (DMI3-5)

A 0.5 L double jacket reactor is charged with 178 g of a solution of di(3,4-dichlorophenyl)borinic acid (0.2 mol) in a THF/toluene mixture (⅔ w/w) and 13 g water. A 10% aqueous solution of sodium hydroxide (32 g) is added to adjust the pH to 7.4. N-(2-Bromo-4-fluorophenyl)-1-methyl-3-(difluoromethyl)-1H-pyrazole-4-carboxamide (56 g, 0.2 mol) is added and, subsequently, the reaction mixture is deoxygenated and heated to 75-80° C. At this temperature a mixture of 0.06 g (0.2 mmol) palladium acetylacetonate and 0.06g (0.2 mmol) tri-tert.-butylphosphonium tetrafluoroborate dissolved in a 1/1 mixture of water and toluene, is charged. The pH is adjusted to 8.0-8.5 and maintained in this range by addition of a 10% w/w sodium hydroxide solution (consumption 98 g). After the end of reaction, the reaction mixture is cooled to 20° C. and the aqueous phase is separated off (195 g). The organic layer (190 g) contains 22% w/w (HPLC) of N-(3′,4′-dichloro-5-fluorobiphenyl-2-yl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide (50% yield). 

1. A process for preparing substituted biphenylanilides of the formula I

Het is a heterocyclyl-residue selected from

wherein “#” indicates the substituted position of the residue; X is hydrogen fluorine or chlorine; R¹ is C₁—C₆-haloalkyl; R² is cyano, nitro, halogen, C₁—C₆-alkyl, C₁—C₆-alkenyl, C₁—C₆-alkynyl, C₁—C₆-alkoxy, C₁—C₆-haloalkyl, (C₁—C₆-alkyl)carbonyl or phenyl; R³ is C₁—C₄-alkyl, C₁—C₄-alkenyl or C₁—C₄-alkynyl; n is 1 , 2 or 3, where in case that n is 2 or 3, the R² radicals may also be different, which comprises reacting a compound of formula II

in which Hal is halogen and X and Het are as defined above, in the presence of a base and of a palladium catalyst selected from the group of: a) palladium-triarylphosphine or -trialkylphosphine complex with palladium in the zero oxidation state, b) salt of palladium in the presence of triaryiphospine or trialkylphosphine as a complex ligand or c) metallic palladium, optionally applied to support, in the presence of triarylphosphine or trialkylphosphine, in a solvent, with a diphenylborinic acid according to formula (III)

in which R² and n are as defined above, where the triarylphosphines or trialkylphosphines used may be substituted.
 2. The process according to claim 1, wherein the compound (II) used is selected from the group consisting of N-(2-chloro-4-fluorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, N-(2-bromo-4-fluorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide, 2-chloro-N-(2-chlorophenyl)pyridine-3-carboxamide and 2-chloro-N-(2-bromo-phenyl)pyridine-3-carboxamide.
 3. The process according to claim 1 or 2, wherein the starting compound (III) is a diphenylborinic acid which is substituted in the 3- and 4-position.
 4. The process according to claims 1 or 2, wherein a diphenylborinic acid (III) is used which bears fluorine or chlorine in the 3- and 4-positions.
 5. The process according to claims 1 or 2, wherein the starting compound (III) is di(3,4-dichlorophenyl)borinic acid.
 6. The process according to claims 1 to 5, wherein the palladium catalyst a) according to claim 1 used is tetrakis(triphenylphosphine)palladium or tetrakis(tri-tert.-butylphosphine)palladium.
 7. The process according to claims 1 to 5, wherein a palladium catalyst b) according to claim 1 is used.
 8. The process according to claims 1 to 5, wherein the palladium catalyst c) according to claim 1 used is metallic palladium on activated carbon in the presence of triphenylphosphine whose phenyl groups are substituted by a total of from 1 to 3 sulfonate groups.
 9. The process as claimed in claim 7, wherein the salt of the palladium catalyst b) used is palladium chloride, palladium acetate, palladium bisacetylacetonate (Pd(acac)₂) or bisacetonitrilepalladium chloride.
 10. The process according to claim 7, wherein a palladium catalyst b) is used for which from 6 to 60 equivalents of triphenylphosphine are used per equivalent of the palladium salt.
 11. The process according to claim 1, wherein from 0.001 to 1.0 mol % of the palladium catalyst is used, based on the amount of compound (II).
 12. The process according to claim 1, wherein the reaction is carried out at a temperature of from 50 to I20° C.
 13. The process according to claim 1, wherein the reaction is carried out in a mixture of water and an organic solvent.
 14. The process according to claim 13, wherein the organic solvent used is an ether.
 15. The process according to claim 1, wherein the reactions are carried out at a pressure of from 1 to 6 bar.
 16. The process according to claim 1, wherein compound (II) is N-(2-chloro-4-fluorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide and compound (III) is di(3,4-dichlorophenyl)borinic acid.
 17. The process according to claim 1, wherein compound (II) is N-(2-chlorophenyl)-3-(difluoromethyl)-1-methyl-1H-pyrazole-4-carboxamide and compound (III) is di(3,4-dichlorophenyl)borinic acid.
 18. The process according to claim 1, wherein compound (II) is 2-chloro-N-(2-bromophenyl)pyridine-3-carboxamide and compound (III) is (4-chlorophenyl)borinic acid. 